A calibration method from the Emerging Radio Systems Group, published in IEEE Microwave and Wireless Technology Letters, estimates the complex excitation of every element in a millimetre-wave phased array from far-field measurements taken while the whole array is radiating — and without assuming anything about how the beamforming circuits behave.
Phased arrays are normally calibrated one channel at a time, with every other element switched off. That is simple, but it does not describe the array as it actually operates: mutual coupling between elements, current loading, and thermal and bias drift inside the beamforming ICs only appear when all the channels are driven together. The paper shows the size of the gap directly — the measured constellation response of a single beamformer channel shifts as more channels on the same chip are enabled.
The method sidesteps it. The array is rotated to a sequence of angles while a fixed far-field receiver records complex transmission coefficients, and the per-element excitations are recovered by solving a linear inverse problem over those measurements. Because every element is live throughout, the result is the array’s real operating state rather than an idealization of it. Earlier active-calibration schemes needed constant error models, pre-calibrated magnitudes or embedded near-field probes; this one needs none of them.
It was validated over the air on a 4 × 4 array at 38.5 GHz, mounted on a two-axis motorized gimbal in an absorber-lined chamber. Radiation patterns reconstructed from the estimated excitations match the measured patterns to a normalized RMS error better than −30 dB; the same reconstruction from element-by-element measurements manages only −8 dB. Used to calibrate the array, the method raises boresight gain by 1.4 dB over passive calibration, improves sidelobe balance by 2.4 dB, and — steering a null at boresight — reaches a null 21.2 dB deeper, with no pointing error.
The work is by Mohammad Abdollah Chalaki, Ahmed Ben Ayed, Patrick Mitran and Slim Boumaiza.
Citation
M. A. Chalaki, A. Ben Ayed, P. Mitran and S. Boumaiza, “Assumption-Free Active Calibration of mm-Wave Phased Arrays Using Excitation Estimation via Far-Field Measurements,” IEEE Microwave and Wireless Technology Letters, vol. 36, no. 6, pp. 938–941, June 2026, doi: 10.1109/LMWT.2026.3678018. Read it on IEEE Xplore →